The present invention relates to a method and apparatus for manufacturing a toothed gear from a disc-shaped material.
The inventor of the present application has heretofore proposed a method of manufacturing a dry plate as disclosed in the Japanese Patent Laid-open Publication No. HEI 4-279239.
The dry plate manufacturing method disclosed in such prior art publication is characterized in that an outer peripheral portion of a disc-shaped material is swaged in its axial direction by means of a swaging die to make the outer peripheral portion thereof thick. An inner side portion of the thus swaged portion is then pressed in the axial direction to form a dish-shaped blank. A support die is the press fitted to one of an outer peripheral portion and an inner peripheral portion and a toothed die is press fitted to the other one thereof so as to form toothed gear an either the outer or inner peripheral portions of the blank. Gear teeth are then formed on either one of these portions by rolling working or machining working.
As the disc-shaped material used for the dry plate manufacturing method in the above prior art, a high carbon steel plate is generally used. A soft steel plate may be used in a case where relatively high strength is not required and necessary strength can be obtainable by a hardening process through swaging working.
In the prior art swaging is performed at room temperature and a crack may be caused in the material by such working. Thus the lifetime of a tool is shortened.
In order to prevent such cracking, there is proposed a method, as disclosed in Japanese Patent Laid-open Publication No. HEI 6-323399, in which a spheroidizing process is required. However, such spheroidizing process involves manufacturing cost increasing, and the material to be used has a limit in its working condition. In addition, much labor is required for plastic deformation due to pressure application, requiring increased working processes and working times, thus providing problems.